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Old 08-09-2022, 08:57 PM   #1
N147JK
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Default 4-Pin Relay Orientation?

The under hood junction box has the relay functions labeled on the lid. But it doesn't indicate anything about the individual pins. Is the top right hole always for relay pin 30? Or, do I recall somehting about the orientation not mattering with 4-pin relays? - Thanks
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Old 08-09-2022, 09:48 PM   #2
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2003 L-Series 3.0L Sedan
Default Re: 4-Pin Relay Orientation?

This may be a tricky question unless familiar with relay pinouts as long as the relay is keyed. There are two 87a relays; a 4-pin and 5-pin relay with the same four pins sharing the same pinouts; 12v control signal and ground on 85 and 86, fused 12v power (hot at all times) and ground on 30 and 87.

If a 4-pin 87a relay is noted/labeled before removing, pinouts on the relay identify female pins to male relay socket terminals on the fuse panel. If a 4-pin relay is inadvertently removed without noting orientation to its socket, there should be a way to determine pinouts on the fuse sockets by measuring for voltage.

Only one socket terminal is HOT whether ignition is turned on or off. This hot socket is fused and can be measured with ignition OFF. Simply probing all four socket terminals should reveal which socket is hot with 12v. Once determined, the relay pinouts should help determine whether its 30 or 87 as one of these two female terminals on the relay mates to the fuse socket having 12v. The other three socket terminals follows the relay pinouts.

An example of a 4-pin 87a relay wiring diagram is below.
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Old 08-09-2022, 10:47 PM   #3
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Default Re: 4-Pin Relay Orientation?

Thank you fdryer for that info - appreciated!

So, pin 30 always goes on the battery power socket. I checked the sockets with the power off. Interestingly, in 2 cases (the 2 smaller relays) there are 2 pins that both have 12 volts on them. One is the horn relay. I found that the horn works exactly the same regardless of which way the relay is inserted. I guess there are normally open and normally closed type relay circuitry.

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Old 08-10-2022, 12:29 AM   #4
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Default Re: 4-Pin Relay Orientation?

What year is your car? There was a similar question in another thread just recently that I posted to, but I can't find that thread. Point is, on my gen1s, #30 socket is not connected to the battery. It is #87 that is "always hot".

The 4-pin relays have the coil and contact pins on a "diagonal pattern", so will operate in either position. I am assuming there is no diode across the coil, which I think is standard for these type auto relays.

PS: never a ground on either 30 or 87...
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Old 08-10-2022, 08:17 AM   #5
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Default Re: 4-Pin Relay Orientation?

Quote:
Originally Posted by billr View Post
what year is your car?
2002 sl1
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Old 08-10-2022, 11:01 AM   #6
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Default Re: 4-Pin Relay Orientation?

Quote:
Originally Posted by billr View Post
...The 4-pin relays have the coil and contact pins on a "diagonal pattern", so will operate in either position. I am assuming there is no diode across the coil, which I think is standard for these type auto relays.

PS: never a ground on either 30 or 87...
You are correct about no ground on 30 or 87. My bad as I meant the ground connection is thru a resistance; horn, fuel pump, cooling fan, ac clutch, evap solenoid, fuel vent valve, etc. My apology as 12v going to ground thru contacts 30 and 87 would be dead short. 12v sent to a fuel pump on one connection and pump connected to ground powers the pump.

The only relay using a diode in parallel (to the coil) is the ac clutch relay.
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Old 08-10-2022, 11:36 AM   #7
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Default Re: 4-Pin Relay Orientation?

Quote:
Originally Posted by N147JK View Post
So, pin 30 always goes on the battery power socket. I checked the sockets with the power off. Interestingly, in 2 cases (the 2 smaller relays) there are 2 pins that both have 12 volts on them. One is the horn relay. I found that the horn works exactly the same regardless of which way the relay is inserted. I guess there are normally open and normally closed type relay circuitry.
All 87a relays are configured (no power to the relay coil) with normally open contacts (30 and 87). A command to send power to the coil closes contacts 30 and 87. Some circuits like the horn need 12v on either 85 or 86 since the horn works without turning on ignition.

If I'm not mistaken, you're examining the relay wiring for the ac clutch. I mentioned leaving the ignition switch OFF when probing for 12v on the four relay socket terminals of the ac relay. If you turn ignition ON, the ignition switch distributes 12v to various circuits, one of them is the ac relay on either 85 or 86. If you have ignition ON, there will be two relay socket terminals with 12v on them. This can confuse anyone unfamiliar with relay circuits. In this case, leave ignition OFF so you won't be misled by a second 12v source on the four relay socket terminals.
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Old 08-12-2022, 09:54 AM   #8
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Default Re: 4-Pin Relay Orientation?

Up until 2000, GM used a 40 amp rely for all things, a four pin and a five pin.

Starting in 2000, Gm cut costs, and started using 25 amp, 30 amp, or 40 amp relays,.

The 25 and 30 are discontinued, but the 40 fits in just fine and works.
Base is the same.
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